This invention relates to improvements in power supplies that provide a number of different direct current voltages by rectifying the outputs of a number of secondary windings of a power transformer. A main output direct current voltage is derived from one secondary winding and regulated by modulating the width of pulses of current flowing in the primary winding of the transformer. Auxiliary direct current output voltages are derived by rectifying the voltage at each of the other secondary windings and each is controlled by its own regulator.
Some regulators for this latter purpose have operated by varying the impedance of a transistor connected in series or shunt with the auxiliary voltage, and whereas such a circuit uses few parts, the fact that it must be able to dissipate any excess energy due to variations in the width of the current pulses in the primary winding caused by the regulation of the main direct-current voltage makes necessary the use of large expensive components.
Greater efficiency has been attained by using a transistor as a switch in a pulse width modulation circuit but more components are required thus increasing cost and size. In addition to the transistor and its control circuits the latter circuit requires a rectifier and filter between the secondary winding and the transistor as well as an output filter between the transistor and the terminals at which the direct current auxiliary voltage appears. Inefficiency is introduced and radiation increased because of the transformation of the power flowing through the circuit from A.C. to D.C. to A.C. and back to D.C.